How do you get your ex off of your back?

4 months ago I broke up with my ex, he wont accept being friends and keeps insisting that we should get back together and is too stubborn to see my side of things. I want to be close, we have too much history to let all of that go, but I am not in a position to be with him. He keeps being ridiculously redundant, and our conversations consist of exhausting debates. I understand that he’s hurt, but I dread talking to him, because I know what I’m in for, and that’s not how I want it to be. How can I explain to him in a way he will understand?